Electrosynthesis System

Abstract

To provide an electrosynthesis system that can realize a long-term use of a catalyst used for a synthesis from a hydrogen gas and a carbon monoxide gas to a hydrocarbon gas, and can improve the synthesis efficiency of the hydrocarbon gas.SOLUTION: An electrosynthesis system supplies a hydrogen gas to synthesis devices through electrolytic devices (52A and 52B) by opening steam flow control valves (81A and 81B) without opening carbon dioxide flow control valves (82A and 82B), when concentration of a carbon dioxide gas in an exhaust gas becomes under a predetermined carbon dioxide concentration threshold level in a state that an oxygen gas is supplied to the synthesis devices (56A and 56B).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrosynthesis system. [Background technology]

[0002] In recent years, efforts to significantly reduce waste generation through waste prevention, reduction, recycling, and reuse have been gaining momentum. Toward this goal, research and development into electrolytic synthesis systems is being conducted. Electrolytic synthesis systems electrolyze carbon dioxide gas and water vapor, and synthesize hydrocarbon gases such as methane from the hydrogen gas and carbon monoxide gas obtained by electrolysis.

[0003] Catalysts are sometimes used to synthesize hydrocarbon gases from hydrogen gas and carbon monoxide gas. In this case, carbon tends to deposit on the catalyst over long periods of use. Carbon deposition on the catalyst reduces the efficiency of hydrocarbon gas synthesis.

[0004] Patent Document 1 below discloses that carbon deposits on a catalyst disappear when the catalyst is brought into contact with air and heated at a predetermined temperature. Therefore, when carbon deposits on a catalyst for synthesizing hydrocarbon gas, the deposited carbon can be removed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-95722 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the carbon deposited on the catalyst is brought into contact with air and heated to a certain temperature, the catalyst tends to oxidize, which reduces the efficiency of hydrocarbon gas synthesis.

[0007] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0008] One aspect of the present invention is an electrolytic synthesis system including an electrolysis device that electrolyzes carbon dioxide gas and water vapor to produce carbon monoxide gas and hydrogen gas, and a synthesis device that synthesizes a hydrocarbon gas from the carbon monoxide gas and the hydrogen gas discharged from the electrolysis device using a catalyst, the system including a steam flow control valve that adjusts the flow rate of the water vapor supplied to the electrolysis device, a carbon dioxide amount control valve that adjusts the flow rate of the carbon dioxide gas supplied to the electrolysis device, a carbon dioxide concentration sensor that measures the concentration of the carbon dioxide gas in the exhaust gas discharged from the synthesis device, and a control device, wherein when the concentration of the carbon dioxide gas in the exhaust gas falls below a predetermined carbon dioxide concentration threshold while oxygen gas is supplied to the synthesis device, the control device opens the steam amount control valve without opening the carbon dioxide amount control valve, and supplies the hydrogen gas to the synthesis device via the electrolysis device. [Effects of the Invention]

[0009] According to the above aspect, hydrogen gas generated in the electrolysis device by electrolysis of water vapor can be supplied from the electrolysis device to the synthesis device. As a result, the catalyst oxidized by combustion of carbon deposited on the catalyst can be reduced by reaction with hydrogen gas. As a result, a decrease in the synthesis efficiency of hydrocarbon gas in the synthesis device can be suppressed. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an electrolytic synthesis system according to an embodiment. [Figure 2] FIG. 2 is a diagram showing the first gas processing mechanism and the second gas processing mechanism. [Figure 3] FIG. 3 is a diagram showing a case where the carbon combustion step is carried out in the second gas treatment mechanism. [Figure 4]FIG. 4 is a diagram showing a case where the catalyst reduction step is carried out in the second gas treatment mechanism. [Figure 5] FIG. 5 is a diagram showing a case where the carbon combustion step is carried out in the first gas treatment mechanism. [Figure 6] FIG. 6 is a diagram showing a case where the catalyst reduction step is carried out in the first gas treatment mechanism. [Figure 7] FIG. 7 is a diagram showing the transition of gas at the fuel electrode of the first electrolysis device or the second electrolysis device. [Figure 8] FIG. 8 is a diagram showing one modified gas processing mechanism. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Embodiment] 1 is a schematic diagram showing the configuration of an electrolytic synthesis system 10 according to an embodiment. The electrolytic synthesis system 10 includes a steam generator 12, a raw material gas concentrator 14, an oxygen-containing gas supplier 16, a first gas treatment mechanism 18A, a second gas treatment mechanism 18B, a heat exchanger 20, a dehumidifier 22, and a separator 24.

[0012] The steam generator 12 is a device that generates water vapor. The steam generator 12 evaporates water supplied from a water source. The water source may be a water purification facility or a water supply tank. The water vapor obtained by the steam generator 12 is supplied to the first gas treatment mechanism 18A via a first steam supply passage 31A. The water vapor obtained by the steam generator 12 is supplied to the second gas treatment mechanism 18B via a second steam supply passage 31B.

[0013] The raw material gas concentrating device 14 is a device that concentrates the raw material gas. The raw material gas concentrating device 14 concentrates the raw material gas in the raw material-containing gas supplied from the raw material gas source, for example, using pressure swing adsorption (PSA). The raw material gas is carbon dioxide gas. The raw material gas source may be a plant facility such as a waste disposal site or a steel mill, or may be a raw material gas tank. The raw material gas concentrated in the raw material gas concentrating device 14 is supplied to the first gas treatment mechanism 18A via the first raw material gas supply path 32A. The raw material gas concentrated in the raw material gas concentrating device 14 is supplied to the second gas treatment mechanism 18B via the second raw material gas supply path 32B.

[0014] The oxygen-containing gas supplier 16 is a device that delivers an oxygen-containing gas containing oxygen gas. The oxygen-containing gas supplier 16 may be a blower. The oxygen-containing gas may be air. The oxygen-containing gas delivered from the oxygen-containing gas supplier 16 is supplied to the first gas treatment mechanism 18A via a first oxygen-containing gas supply path 33A. The oxygen-containing gas delivered from the oxygen-containing gas supplier 16 is supplied to the second gas treatment mechanism 18B via a second oxygen-containing gas supply path 33B.

[0015] The first gas treatment mechanism 18A and the second gas treatment mechanism 18B are mechanisms that selectively perform one of a hydrocarbon production process, a carbon combustion process, and a catalyst reduction process. The hydrocarbon production process is a process in which a catalyst is used to produce hydrocarbon gas from water vapor and carbon dioxide gas. The carbon combustion process is a process in which carbon deposited on the catalyst is reacted with oxygen gas to burn the carbon. The catalyst reduction process is a process in which the catalyst oxidized by carbon combustion is reacted with hydrogen gas to reduce the catalyst.

[0016] The first gas treatment mechanism 18A discharges exhaust gas obtained through the hydrocarbon production process, carbon combustion process, or catalytic reduction process into the first exhaust gas passage 34A. The second gas treatment mechanism 18B discharges exhaust gas obtained through the hydrocarbon production process, carbon combustion process, or catalytic reduction process into the second exhaust gas passage 34B. When the hydrocarbon production process is performed, the exhaust gas contains hydrocarbon gas, water vapor, carbon monoxide gas, and carbon dioxide gas. On the other hand, when the carbon combustion process is performed, the exhaust gas contains water vapor, carbon dioxide gas, and oxygen gas. On the other hand, when the catalytic reduction process is performed, the exhaust gas contains water vapor and hydrogen gas. Details of the first gas treatment mechanism 18A and the second gas treatment mechanism 18B will be described later.

[0017] An exhaust gas merging passage 35 and a refrigerant pipe (not shown) pass through the heat exchanger 20. Exhaust gas supplied from the first gas treatment mechanism 18A via the first exhaust gas passage 34A and exhaust gas supplied from the second gas treatment mechanism 18B via the second exhaust gas passage 34B flow through the exhaust gas merging passage 35. A refrigerant supplied from a refrigerant tank (not shown) flows through the refrigerant pipe. The heat exchanger 20 exchanges heat between the refrigerant and the exhaust gas to cool the exhaust gas.

[0018] The dehumidifier 22 is disposed in the exhaust gas merging path 35 downstream of the heat exchanger 20. The dehumidifier 22 extracts moisture from the exhaust gas. In this embodiment, the dehumidifier 22 cools the exhaust gas to extract the moisture. The dehumidifier 22 discharges the moisture extracted from the exhaust gas into a drainage path 36. The moisture discharged into the drainage path 36 may be returned to the steam generator 12.

[0019] Separator 24 is disposed in exhaust gas merging path 35 downstream of dehumidifier 22. Separator 24 has one or more adsorbents that adsorb specific gases. In this embodiment, separator 24 has a hydrogen adsorbent, a carbon monoxide adsorbent, and a carbon dioxide adsorbent. Separator 24 uses pressure swing adsorption (PSA) to individually separate the hydrogen gas, carbon monoxide gas, and carbon dioxide gas in the exhaust gas. The hydrogen gas separated from the exhaust gas is discharged to hydrogen gas discharge path 37, the carbon monoxide gas separated from the exhaust gas is discharged to carbon monoxide gas discharge path 38, and the carbon dioxide gas separated from the exhaust gas is discharged to carbon dioxide gas discharge path 39.

[0020] As described above, when the hydrocarbon production step is performed in at least one of the first gas treatment mechanism 18A and the second gas treatment mechanism 18B, the exhaust gas contains hydrocarbon gas. In this case, the hydrogen gas, carbon monoxide gas, and carbon dioxide gas in the exhaust gas are separated by the separator 24, so that the hydrocarbon gas in the exhaust gas is concentrated. The concentrated hydrocarbon gas is discharged to the hydrocarbon gas discharge path 40.

[0021] The control device 26 is a device that controls the electrolytic synthesis system 10. The control device 26 causes the first gas treatment mechanism 18A to perform the hydrocarbon production process, the carbon combustion process, or the catalytic reduction process. The control device 26 causes the second gas treatment mechanism 18B to perform the hydrocarbon production process, the carbon combustion process, or the catalytic reduction process. Details of the control by the control device 26 will be described later.

[0022] 2 is a diagram showing the first gas processing mechanism 18A and the second gas processing mechanism 18B. The components of the second gas processing mechanism 18B that correspond to the components of the first gas processing mechanism 18A are given the same numbers and have the letter B instead of A.

[0023] The first gas treatment mechanism 18A includes, as its components, a first heater 50A, a first electrolysis device 52A, a first heat exchanger 54A, a first synthesis device 56A, and a first gas analyzer 58A. The second gas treatment mechanism 18B includes, as its components, a second heater 50B, a second electrolysis device 52B, a second heat exchanger 54B, a second synthesis device 56B, and a second gas analyzer 58B.

[0024] The above-mentioned components provided in the first gas processing mechanism 18A are substantially the same as the above-mentioned components provided in the second gas processing mechanism 18B. Furthermore, the connection relationships between the above-mentioned components provided in the first gas processing mechanism 18A are substantially the same as the connection relationships between the above-mentioned components provided in the second gas processing mechanism 18B. Therefore, hereinafter, a description of the above-mentioned components provided in the second gas processing mechanism 18B and the connection relationships between these components will be omitted.

[0025] The first heater 50A is a heating device. The first heater 50A heats the water vapor supplied to the first electrolysis device 52A. The first heater 50A also heats the raw material gas (carbon dioxide gas) supplied to the first electrolysis device 52A. The downstream end of the first steam supply channel 31A, the downstream end of the first raw material gas supply channel 32A, and the upstream end of the first mixed gas supply channel 41A are arranged on the first heater 50A. The downstream end of the first steam supply channel 31A and the downstream end of the first raw material gas supply channel 32A are connected to the upstream end of the first mixed gas supply channel 41A. The downstream end of the first mixed gas supply channel 41A is connected to the first electrolysis device 52A.

[0026] The first electrolysis device 52A is an electrolysis device that electrolyzes carbon dioxide gas and water vapor. The first electrolysis device 52A has a plurality of electrolysis cells 61. Each electrolysis cell 61 has an electrolyte membrane 62, a fuel electrode 63, and an oxygen electrode 64. The electrolyte membrane 62 is sandwiched between the fuel electrode 63 and the oxygen electrode 64. The electrolyte membrane 62 is, for example, a solid electrolyte membrane such as yttria-stabilized zirconia.

[0027] The fuel electrode 63 may be referred to as a cathode electrode. The fuel electrode 63 is connected to the steam generator 12 via a first mixed gas supply channel 41A and a first steam supply channel 31A. The fuel electrode 63 is also connected to the raw material gas concentrator 14 via a first mixed gas supply channel 41A and a first raw material gas supply channel 32A. The fuel electrode 63 is also connected to the first synthesis device 56A via a first mixed gas discharge channel 42A.

[0028] The oxygen electrode 64 may be referred to as an anode electrode. The oxygen electrode 64 is connected to the oxygen-containing gas supplier 16 via a first oxygen-containing gas supply path 33A. The oxygen electrode 64 is also connected to an oxygen discharge part via a first oxygen-containing gas discharge path 43A. The oxygen discharge part may be an oxygen gas tank or the atmosphere.

[0029] The first heat exchanger 54A is provided between the first electrolysis device 52A and the first synthesis device 56A. The first mixed gas discharge path 42A and a refrigerant pipe (not shown) pass through the first heat exchanger 54A. The first heat exchanger 54A cools the gas supplied to the first synthesis device 56A by exchanging heat between the refrigerant flowing through the refrigerant pipe and the gas flowing through the first mixed gas discharge path 42A. The first heat exchanger 54A can adjust the degree of cooling of the gas in accordance with a temperature specified by the control device 26 (FIG. 1). In this embodiment, the first heat exchanger 54A adjusts the degree of cooling of the gas by increasing or decreasing the flow rate of the refrigerant flowing through the refrigerant pipe.

[0030] The first synthesis device 56A is a synthesis device that synthesizes hydrocarbon gas from carbon monoxide gas and hydrogen gas. Carbon monoxide gas and hydrogen gas are supplied to the first synthesis device 56A from the first electrolysis device 52A when the hydrocarbon production step is carried out in the first gas treatment mechanism 18A. The first synthesis device 56A synthesizes hydrocarbon gas using a catalyst. The catalyst is, for example, a catalyst containing a metal such as nickel.

[0031] When the catalyst is used for a long period of time, carbon may be deposited on the catalyst. In this case, a carbon combustion process is carried out in the first gas treatment mechanism 18A. When the carbon combustion process is carried out, oxygen gas is supplied from the first electrolysis device 52A to the first synthesis device 56A. In this case, carbon dioxide gas and water (water vapor) are produced in the first synthesis device 56A by a combustion reaction between the carbon deposited on the catalyst and the oxygen gas.

[0032] The catalyst tends to be oxidized by a reaction between carbon deposited on the catalyst and oxygen gas. Therefore, in this embodiment, a catalyst reduction step is performed after the carbon combustion step. When the catalyst reduction step is performed, hydrogen gas is supplied to the first synthesis device 56A from the first electrolysis device 52A. In this case, water (water vapor) is generated in the first synthesis device 56A by a reduction reaction between the oxidized catalyst and hydrogen gas.

[0033] The first gas analyzer 58A is provided in the first exhaust gas passage 34A near the first synthesis device 56A. The first gas analyzer 58A includes a hydrocarbon concentration sensor 71, a carbon dioxide concentration sensor 72, a hydrogen concentration sensor 73, and a water vapor concentration sensor 74. The hydrocarbon concentration sensor 71 detects the concentration of hydrocarbon gas in the exhaust gas. The carbon dioxide concentration sensor 72 detects the concentration of carbon dioxide gas in the exhaust gas. The hydrogen concentration sensor 73 detects the concentration of hydrogen gas in the exhaust gas. The water vapor concentration sensor 74 detects the concentration of water vapor in the exhaust gas.

[0034] Next, the control device 26 (FIG. 1) that switches between the hydrocarbon production step, the carbon combustion step, and the catalytic reduction step will be described.

[0035] The control device 26 is a computer that controls the electrosynthesis system 10. The control device 26 includes an operation unit, a storage unit, and a calculation unit. The operation unit is an input device that can receive instructions from an operator. The storage unit can be composed of a volatile memory and a non-volatile memory. Examples of the volatile memory include RAM. Examples of the non-volatile memory include ROM and flash memory. The calculation unit includes a processor such as a CPU or MPU.

[0036] The control device 26 controls multiple valves provided in the first gas treatment mechanism 18A to cause the first gas treatment mechanism 18A to perform the hydrocarbon production process, the carbon combustion process, or the catalytic reduction process. The control device 26 controls multiple valves provided in the second gas treatment mechanism 18B to cause the second gas treatment mechanism 18B to perform the hydrocarbon production process, the carbon combustion process, or the catalytic reduction process. In the drawing, open valves are shown in white, and closed valves are shown in black.

[0037] The multiple valves provided in the first gas treatment mechanism 18A include a first steam amount adjustment valve 81A, a first carbon dioxide amount adjustment valve 82A, a first oxygen on-off valve 83A, a first selector valve 84A, a first oxygen path switching valve 85A, and a first mixed path switching valve 86A. The multiple valves provided in the second gas treatment mechanism 18B include a second steam amount adjustment valve 81B, a second carbon dioxide amount adjustment valve 82B, a second oxygen on-off valve 83B, a second selector valve 84B, a second oxygen path switching valve 85B, and a second mixed path switching valve 86B.

[0038] The valves provided in the first gas processing mechanism 18A and the valves provided in the second gas processing mechanism 18B are substantially the same, so the following description of the valves provided in the second gas processing mechanism 18B will be omitted.

[0039] The first steam flow rate adjustment valve 81A is provided in the first steam supply passage 31A. The first steam flow rate adjustment valve 81A is a flow rate adjustment valve that adjusts the flow rate of steam supplied to the first electrolysis device 52A. The first steam flow rate adjustment valve 81A is opened or closed under the control of the control device 26. The opening amount of the first steam flow rate adjustment valve 81A may be set by the control device 26, or may be set in advance as a default.

[0040] The first carbon dioxide quantity adjustment valve 82A is provided in the first raw material gas supply path 32A. The first carbon dioxide quantity adjustment valve 82A is a flow rate adjustment valve that adjusts the flow rate of carbon dioxide gas supplied to the first electrolysis device 52A. The first carbon dioxide quantity adjustment valve 82A is opened or closed under the control of the control device 26. The amount of opening of the first carbon dioxide quantity adjustment valve 82A may be set by the control device 26, or may be set in advance as a default.

[0041] In this embodiment, the valve opening amounts of the first steam quantity adjustment valve 81A and the first carbon dioxide quantity adjustment valve 82A are set at a ratio according to the type of hydrocarbon gas synthesized in the first synthesis device 56A. For example, if the type of hydrocarbon gas is methane gas, the valve opening amounts of the first steam quantity adjustment valve 81A and the first carbon dioxide quantity adjustment valve 82A are set at a ratio of 3:1. Alternatively, if the type of hydrocarbon gas is methanol, the valve opening amounts of the first steam quantity adjustment valve 81A and the first carbon dioxide quantity adjustment valve 82A are set at a ratio of 2:1. Alternatively, if the type of hydrocarbon gas is ethanol, the valve opening amounts of the first steam quantity adjustment valve 81A and the first carbon dioxide quantity adjustment valve 82A are set at a ratio of 3:2.

[0042] The first oxygen on-off valve 83A is provided in the first oxygen-containing gas supply passage 33A. The first oxygen on-off valve 83A is an electromagnetic valve. The first oxygen on-off valve 83A is opened or closed under the control of the controller .

[0043] The first switching valve 84A is provided in the first oxygen-containing gas discharge path 43A. The first switching valve 84A is, for example, a three-way valve that can switch paths under the control of the control device 26. The first switching valve 84A switches whether or not oxygen gas is supplied to the first synthesis device 56A. This switching is controlled by the control device 26.

[0044] When the first selector valve 84A supplies oxygen gas to the first synthesis device 56A, the oxygen gas flows into a first communication passage 44A branching off from the first oxygen-containing gas discharge passage 43A. In this case, the oxygen gas is supplied to the first synthesis device 56A via a first mixed gas discharge passage 42A to which the downstream end of the first communication passage 44A is connected. On the other hand, when the first selector valve 84A does not supply oxygen gas to the first synthesis device 56A, the oxygen gas flows downstream of the first oxygen-containing gas discharge passage 43A.

[0045] The first oxygen path switching valve 85A is provided in the first oxygen-containing gas discharge path 43A downstream of the first switching valve 84A. The first oxygen path switching valve 85A is, for example, a three-way valve that can switch paths under the control of the control device 26. The first oxygen path switching valve 85A switches whether or not oxygen gas is supplied to the second electrolysis device 52B. This switching is controlled by the control device 26.

[0046] When the first oxygen path switching valve 85A supplies oxygen gas to the second electrolysis device 52B, the oxygen gas flows into the first communication passage 45A branching off from the first oxygen-containing gas discharge passage 43A. In this case, the oxygen gas is supplied to the second electrolysis device 52B via the second oxygen-containing gas supply passage 33B to which the downstream end of the first communication passage 45A is connected. On the other hand, when the first oxygen path switching valve 85A does not supply oxygen gas to the second electrolysis device 52B, the oxygen gas flows downstream of the first oxygen-containing gas discharge passage 43A. In this case, the oxygen gas is supplied to the oxygen discharge section.

[0047] The first mixing path switching valve 86A is provided in the first mixed gas discharge path 42A. The first mixing path switching valve 86A is, for example, a three-way valve that can switch paths under the control of the control device 26. The first mixing path switching valve 86A switches whether or not oxygen gas is supplied to the first synthesis device 56A. This switching is controlled by the control device 26.

[0048] When the first mixing path switching valve 86A supplies oxygen gas to the first synthesis device 56A, the oxygen gas flows from the first communication passage 44A to the first mixed gas discharge path 42A. In this case, the oxygen gas is supplied to the first synthesis device 56A. On the other hand, when the first mixing path switching valve 86A does not supply oxygen gas to the first synthesis device 56A, the gas discharged from the first electrolysis device 52A to the first mixed gas discharge path 42A is supplied to the first synthesis device 56A.

[0049] Next, a case where the control device 26 causes the first gas treatment mechanism 18A to perform the hydrocarbon production step will be described.

[0050] When first gas treatment mechanism 18A is caused to perform the hydrocarbon production step, control device 26 opens first steam amount adjustment valve 81A, first carbon dioxide amount adjustment valve 82A, and first oxygen on-off valve 83A (see FIG. 2). In this case, first electrolysis device 52A performs electrolysis of water vapor supplied from steam generator 12 and carbon dioxide gas supplied from raw material gas concentrating device 14. When electrolysis is performed, carbon monoxide gas and hydrogen gas are produced at fuel electrode 63, and oxygen gas is produced at oxygen electrode 64.

[0051] When first gas treatment mechanism 18A is caused to perform the hydrocarbon production step, control device 26 controls first mixed path switching valve 86A to form a gas path from fuel electrode 63 of first electrolysis device 52A to first synthesis device 56A (see FIG. 2). In this case, carbon monoxide gas and hydrogen gas produced at fuel electrode 63 are supplied to first synthesis device 56A via first mixed gas discharge path 42A. In first synthesis device 56A, hydrocarbon gas is synthesized from carbon monoxide gas and hydrogen gas using a catalyst.

[0052] When the first gas treatment mechanism 18A is to perform the hydrocarbon production process, the control device 26 specifies a first temperature for the first heat exchanger 54A. The first temperature is set to a temperature suitable for the synthesis reaction from carbon monoxide gas and hydrogen gas to hydrocarbon gas. For example, the first temperature is 300°C.

[0053] When the first gas treatment mechanism 18A is caused to perform the hydrocarbon production step, the control device 26 controls the first switching valve 84A and the first oxygen path switching valve 85A to form a gas path from the oxygen electrode 64 of the first electrolysis device 52A to the oxygen discharge part (see FIG. 2). In this case, the oxygen gas produced at the oxygen electrode 64 is supplied to the oxygen discharge part via the first oxygen-containing gas discharge path 43A together with the oxygen-containing gas supplied from the oxygen-containing gas supplier 16. By supplying the oxygen-containing gas from the oxygen-containing gas supplier 16 to the oxygen electrode 64, the oxygen gas produced at the oxygen electrode 64 is prevented from stagnation in the electrolysis cell 61.

[0054] During the hydrocarbon production process in the first gas treatment mechanism 18A, the control device 26 compares the hydrocarbon concentration detected by the hydrocarbon concentration sensor 71 of the first gas analyzer 58A with a predetermined hydrocarbon concentration threshold value.

[0055] Next, a case where the control device 26 causes the second gas treatment mechanism 18B to perform the hydrocarbon production process will be described. When the control device 26 causes the second gas treatment mechanism 18B to perform the hydrocarbon production process, the control device 26 specifies a first temperature for the second heat exchanger 54B, similar to the first gas treatment mechanism 18A. Furthermore, the control device 26 controls a plurality of valves, similar to the first gas treatment mechanism 18A.

[0056] That is, the control device 26 opens the second steam amount adjustment valve 81B, the second carbon dioxide amount adjustment valve 82B, and the second oxygen on-off valve 83B (see FIG. 2). The control device 26 also controls the second mixture path switching valve 86B to form a gas path from the fuel electrode 63 of the second electrolysis device 52B to the second synthesis device 56B (see FIG. 2). The control device 26 also controls the second switching valve 84B and the second oxygen path switching valve 85B to form a gas path from the oxygen electrode 64 of the second electrolysis device 52B to the oxygen discharge section (see FIG. 2). In this case, similar to the first gas treatment mechanism 18A, the second electrolysis device 52B performs electrolysis of water vapor and carbon dioxide gas, and the second synthesis device 56B performs synthesis of hydrocarbon gas.

[0057] During the hydrocarbon production process in the second gas treatment mechanism 18B, the control device 26 compares the hydrocarbon concentration detected by the hydrocarbon concentration sensor 71 of the second gas analyzer 58B with a predetermined hydrocarbon concentration threshold value.

[0058] Next, a case where the control device 26 switches the process that the second gas treatment mechanism 18B is to perform from the hydrocarbon production process to the carbon combustion process will be described.

[0059] When carbon deposits on the catalyst of the second synthesis unit 56B, the efficiency of hydrocarbon gas synthesis in the second synthesis unit 56B decreases, and the hydrocarbon gas concentration in the exhaust gas discharged from the second synthesis unit 56B tends to decrease. Therefore, the more carbon deposits on the catalyst of the second synthesis unit 56B, the greater the degree of decrease in the hydrocarbon gas concentration in the exhaust gas discharged from the second synthesis unit 56B.

[0060] When the hydrocarbon concentration detected by the hydrocarbon concentration sensor 71 of the second gas analyzer 58B falls below the hydrocarbon concentration threshold, the control device 26 determines that the carbon deposited on the catalyst of the second synthesis device 56B needs to be removed. In this case, the control device 26 causes the second gas treatment mechanism 18B to perform the carbon combustion step. Figure 3 is a diagram showing the case where the carbon combustion step is performed in the second gas treatment mechanism 18B.

[0061] When the second gas treatment mechanism 18B is caused to perform the carbon combustion step, the control device 26 closes the second steam amount adjustment valve 81B and the second carbon dioxide amount adjustment valve 82B (see FIG. 3). In this case, water vapor and carbon dioxide gas are not supplied to the fuel electrode 63 of the second electrolysis device 52B. Therefore, electrolysis of water vapor and carbon dioxide gas is not performed in the second electrolysis device 52B, and synthesis of hydrocarbon gas is not performed in the second synthesis device 56B.

[0062] When the second gas treatment mechanism 18B is caused to perform the carbon combustion process, the control device 26 switches the temperature designated for the second heat exchanger 54B from the first temperature to a second temperature. The second temperature is set to a temperature suitable for the combustion reaction between the carbon deposited on the catalyst and oxygen gas. The second temperature is higher than the first temperature. For example, the second temperature is 500°C.

[0063] When the second gas treatment mechanism 18B is caused to perform the carbon combustion step, the control device 26 closes the second oxygen on-off valve 83B (see FIG. 3). The control device 26 also controls the first oxygen path switching valve 85A to form a gas path from the oxygen electrode 64 of the first electrolysis device 52A to the second electrolysis device 52B (see FIG. 3). The control device 26 also controls the second switching valve 84B and the second mixed path switching valve 86B to form a gas path from the oxygen electrode 64 of the second electrolysis device 52B to the second synthesis device 56B (see FIG. 3). In this case, oxygen gas generated in the first electrolysis device 52A is supplied to the second synthesis device 56B. The oxygen gas flows sequentially through the first oxygen-containing gas discharge path 43A, the first communication path 45A, the second oxygen-containing gas supply path 33B, the second oxygen-containing gas discharge path 43B, the second communication path 44B, and the second mixed gas discharge path 42B.

[0064] During electrolysis in the first electrolysis device 52A, the first electrolysis device 52A reaches a high temperature of approximately 700°C to 800°C. Therefore, the oxygen gas generated in the first electrolysis device 52A is at a high temperature. By passing the high-temperature oxygen gas through the second electrolysis device 52B before being supplied to the second synthesis device 56B, it is possible to warm up the second electrolysis device 52B while electrolysis is stopped. Therefore, compared to when the high-temperature oxygen gas does not pass through the second electrolysis device 52B, the second electrolysis device 52B can be restored and electrolysis can be resumed in the second electrolysis device 52B earlier.

[0065] When oxygen gas is supplied to the second synthesis device 56B, the amount of carbon deposited on the catalyst of the second synthesis device 56B is reduced by a combustion reaction with the oxygen gas. During the carbon combustion process in the second gas treatment mechanism 18B, the control device 26 compares the carbon dioxide concentration detected by the carbon dioxide concentration sensor 72 of the second gas analyzer 58B with a predetermined carbon dioxide concentration threshold.

[0066] Next, a case where the control device 26 switches the process that the second gas treatment mechanism 18B is to perform from the carbon combustion process to the catalytic reduction process will be described.

[0067] When the carbon dioxide concentration falls below the carbon dioxide concentration threshold, controller 26 determines that the amount of carbon deposited on the catalyst in second synthesis device 56B has decreased to a level that has little effect on the synthesis of hydrocarbon gas. In this case, controller 26 causes second gas treatment mechanism 18B to perform a catalyst reduction step. Figure 4 is a diagram showing a case where the catalyst reduction step is performed in second gas treatment mechanism 18B.

[0068] When the second gas treatment mechanism 18B is caused to perform the catalytic reduction step, the controller 26 opens the second steam amount adjustment valve 81B while keeping the second carbon dioxide amount adjustment valve 82B closed (see FIG. 4). In this case, water vapor is supplied to the fuel electrode 63 of the second electrolysis device 52B, but carbon dioxide gas is not supplied. Therefore, electrolysis of water vapor is performed in the second electrolysis device 52B.

[0069] When the second gas treatment mechanism 18B is caused to perform the catalyst reduction process, the control device 26 switches the temperature designated for the second heat exchanger 54B from the second temperature to a third temperature. The third temperature is set to a temperature suitable for the reduction reaction between the catalyst oxidized in the carbon combustion process and hydrogen gas. The third temperature is higher than the first temperature and lower than the second temperature. For example, the third temperature is 400°C.

[0070] When the second gas treatment mechanism 18B is caused to perform the catalytic reduction step, the control device 26 opens the second oxygen on-off valve 83B (see FIG. 4). The control device 26 also controls the second switching valve 84B to form a gas path from the oxygen electrode 64 of the second electrolysis device 52B to the oxygen discharge section (see FIG. 4). The control device 26 also controls the second mixed path switching valve 86B to form a gas path from the fuel electrode 63 of the second electrolysis device 52B to the second synthesis device 56B (see FIG. 4). In this case, hydrogen gas produced by electrolysis of water vapor in the second electrolysis device 52B is supplied to the second synthesis device 56B via the second mixed gas discharge path 42B.

[0071] When hydrogen gas is supplied to second synthesis device 56B, the catalyst that was oxidized in the carbon combustion process reacts with the hydrogen gas and is reduced, gradually returning to its pre-oxidized state. During the catalyst reduction process in second gas treatment mechanism 18B, control device 26 compares the hydrogen concentration detected by hydrogen concentration sensor 73 of second gas analyzer 58B with a predetermined hydrogen concentration threshold.

[0072] If the hydrogen concentration exceeds the hydrogen concentration threshold, the controller 26 determines that the reduction of the oxidized catalyst has been performed to an extent that the reduction has little effect on the synthesis of hydrocarbon gases, and in this case, the controller 26 causes the second gas treatment mechanism 18B to perform the hydrocarbon production step.

[0073] The control device 26 may determine, based on the water vapor concentration in the exhaust gas, whether the oxidized catalyst has been reduced to a level that has little effect on the synthesis of hydrocarbon gases. In this case, while the catalyst reduction step is being performed in the second gas treatment mechanism 18B, the control device 26 compares the water vapor concentration detected by the water vapor concentration sensor 74 of the second gas analyzer 58B with a predetermined water vapor concentration threshold. When the water vapor concentration falls below the water vapor concentration threshold, the control device 26 causes the second gas treatment mechanism 18B to perform the hydrocarbon production step.

[0074] Next, a case where the control device 26 switches the process that the first gas treatment mechanism 18A is to perform from the hydrocarbon production process to the carbon combustion process will be described.

[0075] When the hydrocarbon concentration detected by the hydrocarbon concentration sensor 71 of the first gas analyzer 58A falls below the hydrocarbon concentration threshold, the control device 26 determines that the carbon deposited on the catalyst of the first synthesis device 56A needs to be removed. In this case, the control device 26 causes the first gas treatment mechanism 18A to perform the carbon combustion step. Figure 5 is a diagram showing a case where the carbon combustion step is performed in the first gas treatment mechanism 18A.

[0076] When first gas treatment mechanism 18A is caused to perform the carbon combustion step, controller 26 switches the temperature designated for first heat exchanger 54A from the first temperature to the second temperature. Controller 26 also closes first steam amount control valve 81A and first carbon dioxide amount control valve 82A (see FIG. 5). In this case, electrolysis of water vapor and carbon dioxide gas is not performed in first electrolysis device 52A, and synthesis of hydrocarbon gas is not performed in first synthesis device 56A.

[0077] When the first gas treatment mechanism 18A is caused to perform the carbon combustion process, the control device 26 closes the first oxygen on-off valve 83A (see FIG. 5). The control device 26 also controls the second oxygen path switching valve 85B to form a gas path from the oxygen electrode 64 of the second electrolysis device 52B to the first electrolysis device 52A (see FIG. 5). The control device 26 also controls the first switching valve 84A and the first mixed path switching valve 86A to form a gas path from the oxygen electrode 64 of the first electrolysis device 52A to the first synthesis device 56A (see FIG. 5). In this case, oxygen gas generated in the second electrolysis device 52B is supplied to the first synthesis device 56A. The oxygen gas flows sequentially through the second oxygen-containing gas discharge path 43B, the second communication path 45B, the first oxygen-containing gas supply path 33A, the first oxygen-containing gas discharge path 43A, the first communication path 44A, and the first mixed gas discharge path 42A.

[0078] When oxygen gas is supplied to the first synthesis device 56A, the carbon deposited on the catalyst of the first synthesis device 56A is reduced by a combustion reaction with the oxygen gas. During the carbon combustion process in the first gas treatment mechanism 18A, the control device 26 compares the carbon dioxide concentration detected by the carbon dioxide concentration sensor 72 of the first gas analyzer 58A with a predetermined carbon dioxide concentration threshold.

[0079] Next, a case where the control device 26 switches the process that the first gas treatment mechanism 18A is to perform from the carbon combustion process to the catalytic reduction process will be described.

[0080] When the carbon dioxide concentration falls below the carbon dioxide concentration threshold, controller 26 determines that the amount of carbon deposited on the catalyst in first synthesis device 56A has decreased to a level that has little effect on the synthesis of hydrocarbon gas. In this case, controller 26 causes first gas treatment mechanism 18A to perform a catalyst reduction step. Figure 6 is a diagram showing a case where the catalyst reduction step is performed in first gas treatment mechanism 18A.

[0081] When first gas treatment mechanism 18A is caused to perform the catalytic reduction step, controller 26 switches the temperature designated for first heat exchanger 54A from the second temperature to the third temperature. Controller 26 also opens first steam flow control valve 81A while keeping first carbon dioxide flow control valve 82A closed (see FIG. 6). In this case, water vapor is supplied to fuel electrode 63 of first electrolysis device 52A, but carbon dioxide gas is not supplied. Therefore, water vapor electrolysis is performed in first electrolysis device 52A.

[0082] When the first gas treatment mechanism 18A is caused to perform the catalytic reduction step, the control device 26 opens the first oxygen on-off valve 83A (see FIG. 6). The control device 26 also controls the first switching valve 84A to form a gas path from the oxygen electrode 64 of the first electrolysis device 52A to the oxygen discharge section (see FIG. 6). The control device 26 also controls the first mixed path switching valve 86A to form a gas path from the fuel electrode 63 of the first electrolysis device 52A to the first synthesis device 56A (see FIG. 6). In this case, hydrogen gas produced by electrolysis of water vapor in the first electrolysis device 52A is supplied to the first synthesis device 56A via the first mixed gas discharge path 42A.

[0083] When hydrogen gas is supplied to first synthesis device 56A, the catalyst that was oxidized in the carbon combustion process reacts with the hydrogen gas and is reduced, gradually returning to its pre-oxidized state. During the catalyst reduction process in first gas treatment mechanism 18A, control device 26 compares the hydrogen concentration detected by hydrogen concentration sensor 73 of first gas analyzer 58A with a predetermined hydrogen concentration threshold.

[0084] If the hydrogen concentration exceeds the hydrogen concentration threshold, the control device 26 determines that the oxidized catalyst has been reduced to a degree that has little effect on the synthesis of hydrocarbon gas. In this case, the control device 26 causes the first gas treatment mechanism 18A to perform the hydrocarbon production step.

[0085] The control device 26 may determine, based on the water vapor concentration in the exhaust gas, whether the oxidized catalyst has been reduced to a level that has little effect on the synthesis of hydrocarbon gases. In this case, while the catalyst reduction step is being performed in the first gas treatment mechanism 18A, the control device 26 compares the water vapor concentration detected by the water vapor concentration sensor 74 of the first gas analyzer 58A with a predetermined water vapor concentration threshold. When the water vapor concentration falls below the water vapor concentration threshold, the control device 26 causes the first gas treatment mechanism 18A to perform the hydrocarbon production step.

[0086] As described above, in this embodiment, while carbon dioxide gas and water vapor are being supplied to the first electrolysis device 52A, the control device 26 monitors the hydrocarbon concentration in the exhaust gas discharged from the first synthesis device 56A. When the hydrocarbon concentration falls below a predetermined hydrocarbon concentration threshold, the control device 26 closes the first steam quantity control valve 81A and the first carbon dioxide quantity control valve 82A to stop the supply of carbon dioxide gas and water vapor. Thereafter, the control device 26 controls the first switching valve 84A and the first mixing passage switching valve 86A to supply oxygen gas to the first synthesis device 56A. This allows carbon deposited on the catalyst provided in the first synthesis device 56A to be burned by the oxygen gas.

[0087] Furthermore, in this embodiment, while oxygen gas is being supplied to the first synthesis device 56A, the control device 26 monitors the carbon dioxide concentration in the exhaust gas discharged from the first synthesis device 56A. When the carbon dioxide concentration falls below a predetermined carbon dioxide concentration threshold, the control device 26 opens the first steam quantity adjustment valve 81A without opening the first carbon dioxide quantity adjustment valve 82A to supply steam to the first electrolysis device 52A. This allows hydrogen gas generated in the first electrolysis device 52A by electrolysis of the steam to be supplied from the first electrolysis device 52A to the first synthesis device 56A. As a result, the catalyst that has been oxidized by the combustion of carbon deposited on the catalyst can be reduced by reaction with the hydrogen gas.

[0088] Furthermore, in this embodiment, the control device 26 switches the temperature designated for the first heat exchanger 54A depending on the type of gas supplied to the first synthesis device 56A, thereby allowing each of a plurality of different chemical reactions to be appropriately carried out in the first synthesis device 56A.

[0089] Meanwhile, while carbon dioxide gas and water vapor are being supplied to the second electrolysis device 52B, the control device 26 monitors the hydrocarbon concentration in the exhaust gas discharged from the second synthesis device 56B. When the hydrocarbon concentration in the exhaust gas discharged from the second synthesis device 56B falls below a predetermined hydrocarbon concentration threshold, the control device 26 closes the second steam quantity control valve 81B and the second carbon dioxide quantity control valve 82B to stop the supply of carbon dioxide gas and water vapor. Thereafter, the control device 26 opens the second switching valve 84B to supply oxygen gas to the second synthesis device 56B. This allows carbon deposited on a catalyst provided in the second synthesis device 56B to be burned by the oxygen gas.

[0090] Furthermore, in this embodiment, while oxygen gas is being supplied to the second synthesis device 56B, the control device 26 monitors the carbon dioxide concentration in the exhaust gas discharged from the second synthesis device 56B. When the carbon dioxide concentration falls below a predetermined carbon dioxide concentration threshold, the control device 26 opens the second steam quantity control valve 81B without opening the second carbon dioxide quantity control valve 82B to supply steam to the second electrolysis device 52B. This allows hydrogen gas generated in the second electrolysis device 52B by electrolysis of the steam to be supplied from the second electrolysis device 52B to the second synthesis device 56B. As a result, the catalyst that has been oxidized by the combustion of carbon deposited on the catalyst can be reduced by reaction with the hydrogen gas.

[0091] Furthermore, in this embodiment, the control device 26 switches the temperature designated for the second heat exchanger 54B depending on the type of gas supplied to the second synthesis device 56B, thereby allowing each of the multiple different chemical reactions to be appropriately carried out in the second synthesis device 56B.

[0092] 7 is a diagram showing the transition of gas at the anode 63 of the first electrolysis device 52A or the second electrolysis device 52B. As described above, when transitioning from the hydrocarbon production process to the carbon combustion process, the first steam quantity control valve 81A (or the second steam quantity control valve 81B) and the first carbon dioxide quantity control valve 82A (or the second carbon dioxide quantity control valve 82B) are closed. In this embodiment, the timing T1 at which the first steam quantity control valve 81A (or the second steam quantity control valve 81B) is closed is later than the timing T2 at which the first carbon dioxide quantity control valve 82A (second carbon dioxide quantity control valve 82B) is closed.

[0093] That is, the control device 26 closes the first steam amount adjustment valve 81A (or the second steam amount adjustment valve 81B) after closing the first carbon dioxide amount adjustment valve 82A (or the second carbon dioxide amount adjustment valve 82B). This allows the carbon dioxide gas and carbon monoxide gas remaining in the fuel electrode 63 to be discharged from the fuel electrode 63 by water vapor. Therefore, compared to when the adjustment valves are closed at the same timing, it is possible to increase the efficiency of water electrolysis at the fuel electrode 63, which produces hydrogen gas used in the catalytic reduction step performed after the carbon combustion step. As a result, it is possible to shorten the time required for the catalytic reduction step.

[0094] [Modification] The above embodiment may be modified as follows.

[0095] (Variation 1) The control device 26 may adjust the flow rate of oxygen gas supplied to the first synthesis device 56A or the second synthesis device 56B. In this case, an oxygen concentration sensor and an oxygen amount adjustment valve are provided in each of the first communication passage 44A and the second communication passage 44B. The oxygen amount adjustment valve is disposed downstream of the oxygen concentration sensor.

[0096] The oxygen concentration sensor is a sensor that detects the concentration of oxygen gas in the oxygen-containing gas flowing through the first communication passage 44A or the second communication passage 44B. The oxygen amount regulating valve is a flow rate regulating valve that regulates the flow rate of oxygen gas supplied to the first synthesis device 56A or the second synthesis device 56B.

[0097] When the second gas treatment mechanism 18B is caused to perform the carbon combustion process (see FIG. 3), the control device 26 uses an oxygen concentration sensor provided in the second communication passage 44B to control the aperture of the oxygen amount adjustment valve provided in the second communication passage 44B. In this case, the control device 26 reduces the aperture of the oxygen amount adjustment valve as the concentration of oxygen gas detected by the oxygen concentration sensor increases. This allows oxygen gas to be supplied to the second synthesis device 56B in just the right amount.

[0098] On the other hand, when first gas treatment mechanism 18A is caused to perform the carbon combustion step (see FIG. 5), control device 26 uses an oxygen concentration sensor provided in first communication passage 44A to control the aperture of the oxygen amount adjustment valve provided in first communication passage 44A. In this case, control device 26 reduces the aperture of the oxygen amount adjustment valve as the concentration of oxygen gas detected by the oxygen concentration sensor increases. This allows oxygen gas to be supplied to first synthesis device 56A in just the right amount.

[0099] (Variation 2) A plurality of sets of the first gas processing mechanism 18A and the second gas processing mechanism 18B may be provided.

[0100] (Variation 3) The control device 26 may alternately perform the carbon combustion process and catalytic reduction process in the first gas treatment mechanism 18A and the carbon combustion process and catalytic reduction process in the second gas treatment mechanism 18B per unit time. In this case, the hydrocarbon concentration sensor 71 can be removed. Furthermore, since the control device 26 does not have to compare the hydrocarbon concentration detected by the hydrocarbon concentration sensor 71 with the hydrocarbon concentration threshold value, the processing load on the control device 26 can be reduced.

[0101] (Variation 4) One of the first gas processing mechanism 18A and the second gas processing mechanism 18B may be removed. Fig. 8 is a diagram showing one gas processing mechanism 18 according to a modified example. In Fig. 8, the "first" and "second" and the symbols "A" and "B" that are added to the names of the components in the embodiment have been removed.

[0102] In this modification, oxygen gas generated in one of the first gas processing mechanism 18A and the second gas processing mechanism 18B is not supplied to the other of the first gas processing mechanism 18A and the second gas processing mechanism 18B. Therefore, in the gas processing mechanism 18, the first oxygen path switching valve 85A (or the second oxygen path switching valve 85B), the first mixing path switching valve 86A (or the second mixing path switching valve 86B), the first communication passage 44A (or the second communication passage 44B), and the first communication passage 45A (or the second communication passage 45B) are disconnected.

[0103] On the other hand, the gas treatment mechanism 18 is provided with a connecting pipe 90 that branches off from the oxygen-containing gas discharge passage 43 and is connected to the synthesis device 56 via a heat exchanger 54 .

[0104] The control of the gas processing mechanism 18 by the control device 26 is the same as in the above embodiment, but will be briefly explained below. When the gas processing mechanism 18 is caused to perform the hydrocarbon production step, the control device 26 specifies a first temperature for the heat exchanger 54. The control device 26 also opens the steam amount adjustment valve 81, the carbon dioxide amount adjustment valve 82, and the oxygen on-off valve 83 (see FIG. 8). In addition, the control device 26 controls the switching valve 84 to form a gas path from the oxygen electrode 64 to the oxygen discharge section.

[0105] When the hydrocarbon concentration in the exhaust gas discharged from the synthesis unit 56 falls below the hydrocarbon concentration threshold, the control unit 26 switches the temperature specified for the heat exchanger 54 from the first temperature to the second temperature. The control unit 26 also closes the steam amount adjustment valve 81 and the carbon dioxide amount adjustment valve 82. The control unit 26 also controls the switching valve 84 to form a gas path from the oxygen electrode 64 to the synthesis unit 56.

[0106] When the carbon dioxide concentration in the exhaust gas discharged from the synthesis device 56 falls below the carbon dioxide concentration threshold, the control device 26 switches the temperature specified for the heat exchanger 54 from the second temperature to the third temperature. The control device 26 also opens the steam amount control valve 81 while keeping the carbon dioxide amount control valve 82 closed. The control device 26 also controls the switching valve 84 to form a gas path from the oxygen electrode 64 to the oxygen discharge section.

[0107] In this way, even if one of the first gas treatment mechanism 18A and the second gas treatment mechanism 18B is removed, the control by the control device 26 is the same as in the above embodiment. Therefore, even with one gas treatment mechanism 18, the same effects as in the above embodiment can be obtained.

[0108] (Variation 5) The first communication passage 44A or the second communication passage 44B may be replaced with a connecting pipe 90. In this case, the first mixing passage switching valve 86A or the second mixing passage switching valve 86B can be removed.

[0109] The invention and its effects that can be understood from the above description will be described below.

[0110] (1) The present invention provides an electrolytic synthesis system (10) including an electrolysis device (52, 52A, 52B) that electrolyzes carbon dioxide gas and water vapor to produce carbon monoxide gas and hydrogen gas, and a synthesis device (56, 56A, 56B) that synthesizes a hydrocarbon gas from the carbon monoxide gas and the hydrogen gas discharged from the electrolysis device using a catalyst. The electrolytic synthesis system includes a steam flow control valve (81, 81A, 81B) that adjusts the flow rate of the water vapor supplied to the electrolysis device, a carbon dioxide flow control valve (82, 82A, 82B) that adjusts the flow rate of the carbon dioxide gas supplied to the electrolysis device, a carbon dioxide concentration sensor (72) that measures the concentration of the carbon dioxide gas in the exhaust gas discharged from the synthesis device, and a control device (26). When the concentration of the carbon dioxide gas in the exhaust gas falls below a predetermined carbon dioxide concentration threshold while oxygen gas is being supplied to the synthesis device, the control device opens the steam quantity control valve without opening the carbon dioxide quantity control valve, and supplies the hydrogen gas to the synthesis device via the electrolysis device.

[0111] This allows hydrogen gas generated in the electrolysis device by electrolysis of water vapor to be supplied from the electrolysis device to the synthesis device. As a result, the catalyst oxidized by the combustion of carbon deposited on the catalyst can be reduced by reaction with hydrogen gas. As a result, a decrease in the efficiency of hydrocarbon gas synthesis by the synthesis device can be suppressed. In addition, the hydrogen gas supplied to the synthesis device can be heated by the electrolysis device, which becomes hot during electrolysis. As a result, there is no need to use a heater or the like, and this is more efficient than when hydrogen gas is supplied to the synthesis device without going through the electrolysis device.

[0112] (2) The present invention provides the electrolytic synthesis system described in (1) above, further comprising at least one of a hydrogen concentration sensor (73) that measures the concentration of the hydrogen gas in the exhaust gas and a water vapor concentration sensor (74) that measures the concentration of the water vapor in the exhaust gas. When the concentration of the hydrogen gas in the exhaust gas exceeds a predetermined hydrogen concentration threshold or when the concentration of the water vapor in the exhaust gas falls below a predetermined water vapor concentration threshold while the oxygen gas is being supplied to the synthesis device, the control device may open the steam amount control valve and the carbon dioxide amount control valve to start supplying the carbon dioxide gas and the water vapor to the electrolysis device. This prevents the hydrogen gas from being continuously supplied even when the catalyst is reduced. As a result, the utilization efficiency of the hydrogen gas can be improved.

[0113] (3) The present invention may provide the electrolytic synthesis system described in (1) above, further comprising a hydrocarbon concentration sensor (71) that measures the concentration of the hydrocarbon gas in the exhaust gas and a switching valve (84, 84A, 84B) that selectively switches whether or not to supply the oxygen gas to the synthesis device, wherein when the concentration of the hydrocarbon gas falls below a predetermined hydrocarbon concentration threshold while the carbon monoxide gas and the hydrogen gas are being supplied to the synthesis device, the control device may close the steam flow control valve and the carbon dioxide flow control valve to stop the supply of the carbon dioxide gas and the water vapor to the electrolysis device, and after the supply of the carbon dioxide gas and the water vapor is stopped, the control device may control the switching valve to supply the oxygen gas to the synthesis device. This allows carbon deposited on a catalyst provided in the synthesis device to be burned by the oxygen gas.

[0114] (4) The present invention provides the electrolytic synthesis system according to (3) above, wherein the control device may stop the supply of water vapor after stopping the supply of carbon dioxide gas. This allows the carbon dioxide gas and carbon monoxide gas remaining in the electrolysis device to be pushed out of the electrolysis device by the water vapor. Therefore, compared to when the timing for stopping the supply of carbon dioxide gas and the timing for stopping the supply of water vapor are the same, the efficiency of water electrolysis in the electrolysis device, which produces hydrogen gas used in the catalytic reduction step performed after the carbon combustion step, can be improved. As a result, the time required for the catalytic reduction step can be shortened.

[0115] (5) The present invention provides the electrolytic synthesis system according to (3), further comprising a heat exchanger (54, 54A, 54B) disposed between the electrolytic device and the synthesis device for cooling the gas supplied from the electrolytic device to the synthesis device, wherein the heat exchanger is capable of adjusting the degree of cooling of the gas in accordance with a temperature designated by the control device, and the control device may switch the temperature designated to the heat exchanger in accordance with the type of the gas. This allows each of a plurality of different chemical reactions to be appropriately carried out in the synthesis device.

[0116] (6) The present invention provides the electrolytic synthesis system according to (3), wherein a plurality of the electrolytic devices, the synthesis devices, and the switching valves are provided, a first synthesis device (56A) that is one of the plurality of synthesis devices synthesizes the hydrocarbon gas from the carbon monoxide gas and the hydrogen gas discharged from a first electrolysis device (52A) that is one of the plurality of electrolysis devices, using a catalyst, a second synthesis device (56B) that is another of the plurality of synthesis devices synthesizes the hydrocarbon gas from the carbon monoxide gas and the hydrogen gas discharged from a second electrolysis device (52B) that is another of the plurality of electrolysis devices, using a catalyst, and a first switching valve (84A) that is one of the plurality of switching valves selectively switches whether or not the oxygen gas generated secondarily by the electrolysis in the first electrolysis device is supplied to the second synthesis device, A second switching valve (84B) that is one of the plurality of switching valves may alternatively switch whether or not to supply the oxygen gas that is by-produced by the electrolysis in the second electrolysis device to the first synthesis device, and when the concentration of the hydrocarbon gas in the exhaust gas discharged from the first synthesis device falls below a predetermined hydrocarbon concentration threshold while the carbon monoxide gas and the hydrogen gas are supplied to the synthesis device, the control device may control the second switching valve to supply the oxygen gas to the first synthesis device, and when the concentration of the hydrocarbon gas in the exhaust gas discharged from the second synthesis device falls below a predetermined hydrocarbon concentration threshold while the carbon monoxide gas and the hydrogen gas are supplied to the synthesis device, the control device may control the first switching valve to supply the oxygen gas to the second synthesis device.

[0117] This can improve the efficiency of oxygen gas utilization. Also, oxygen gas warmed by the first electrolysis device where electrolysis is performed can be supplied to the second synthesis device via the second electrolysis device where electrolysis is stopped. Similarly, oxygen gas warmed by the second electrolysis device where electrolysis is performed can be supplied to the first synthesis device via the first electrolysis device where electrolysis is stopped. Therefore, the electrolysis device where electrolysis is stopped can be quickly restored and electrolysis can be resumed by the electrolysis device.

[0118] The present invention is not limited to the above disclosure, and various configurations can be adopted without departing from the gist of the present invention. [Explanation of symbols]

[0119] 10...Electrolytic synthesis system 12...Steam generator 14... Raw material gas concentrator 16... Oxygen-containing gas supplier 18 (18A, 18B)...gas processing mechanism (first gas processing mechanism, second gas processing mechanism) 20...Heat exchanger 22...Dehumidifier 24...Separator 26...Control device 52 (52A, 52B)...Electrolyzer (1st electrolyzer, 2nd electrolyzer) 54 (54A, 54B)...Heat exchanger (1st heat exchanger, 2nd heat exchanger) 56 (56A, 56B)...Synthesizer (1st synthesizer, 2nd synthesizer) 58 (58A, 58B)...Gas analyzer (first gas analyzer, second gas analyzer) 63...Fuel electrode 64...Oxygen electrode 71...Hydrocarbon concentration sensor 72...Carbon dioxide concentration sensor 73...Hydrogen concentration sensor 74...Water vapor concentration sensor 81 (81A, 81B)...Steam flow control valve (first steam flow control valve, second steam flow control valve) 82 (82A, 82B)... Carbon dioxide amount adjustment valve (first carbon dioxide amount adjustment valve, second carbon dioxide amount adjustment valve) 83 (83A, 83B)...Oxygen on-off valve (first oxygen on-off valve, second oxygen on-off valve) 84 (84A, 84B)...Switching valve (first switching valve, second switching valve) 85 (85A, 85B)...Oxygen path switching valve (first oxygen path switching valve, second oxygen path switching valve) 86 (86A, 86B)... Mixing channel switching valve (first mixing channel switching valve, second mixing channel switching valve)

Claims

1. An electrolytic synthesis system including: an electrolysis device that is supplied with oxygen gas and electrolyzes carbon dioxide gas and water vapor to produce carbon monoxide gas and hydrogen gas; and a synthesis device that synthesizes a hydrocarbon gas from the carbon monoxide gas and the hydrogen gas discharged from the electrolysis device using a catalyst, a steam amount regulating valve for regulating the flow rate of the steam supplied to the electrolysis device; a carbon dioxide amount regulating valve for regulating the flow rate of the carbon dioxide gas supplied to the electrolysis device; a carbon dioxide concentration sensor that measures the concentration of the carbon dioxide gas in the exhaust gas discharged from the synthesis device; a control device; a switching valve that selectively switches whether or not the oxygen gas is supplied to the synthesis apparatus; Equipped with when the electrolysis is not performed in the electrolysis device, the control device closes the steam amount regulating valve and the carbon dioxide amount regulating valve, and controls the switching valve to supply the oxygen gas supplied to the electrolysis device to the synthesis device; an electrolytic synthesis system in which, when the concentration of the carbon dioxide gas in the exhaust gas falls below a predetermined carbon dioxide concentration threshold while the oxygen gas is being supplied from the electrolysis device to the synthesis device, the control device opens the steam amount control valve without opening the carbon dioxide amount control valve, and supplies the hydrogen gas to the synthesis device via the electrolysis device.

2. 2. The electrosynthesis system according to claim 1, The exhaust gas control system further includes at least one of a hydrogen concentration sensor that measures the concentration of the hydrogen gas in the exhaust gas and a water vapor concentration sensor that measures the concentration of the water vapor in the exhaust gas, an electrolytic synthesis system in which, when the concentration of the hydrogen gas in the exhaust gas exceeds a predetermined hydrogen concentration threshold or the concentration of the water vapor in the exhaust gas falls below a predetermined water vapor concentration threshold while the oxygen gas is supplied to the synthesis device, the control device opens the steam amount control valve and the carbon dioxide amount control valve to start supplying the carbon dioxide gas and the water vapor to the electrolysis device.

3. 2. The electrosynthesis system according to claim 1, further comprising a hydrocarbon concentration sensor that measures the concentration of the hydrocarbon gas in the exhaust gas; when the concentration of the hydrocarbon gas falls below a predetermined hydrocarbon concentration threshold while the carbon monoxide gas and the hydrogen gas are being supplied to the synthesis device, the control device closes the steam amount control valve and the carbon dioxide amount control valve to stop the supply of the carbon dioxide gas and the water vapor to the electrolysis device; After the supply of the carbon dioxide gas and the water vapor is stopped, the control device controls the switching valve to supply the oxygen gas to the synthesis device.

4. 4. The electrolytic synthesis system according to claim 3, The control device stops the supply of the water vapor after stopping the supply of the carbon dioxide gas.

5. 4. The electrolytic synthesis system according to claim 3, a heat exchanger provided between the electrolysis device and the synthesis device to cool the gas supplied from the electrolysis device to the synthesis device; the heat exchanger is capable of adjusting the degree of cooling of the gas in accordance with a temperature designated by the control device; The control device switches the temperature specified for the heat exchanger depending on the type of the gas.

6. 4. The electrolytic synthesis system according to claim 3, a plurality of the electrolysis devices, the synthesis devices, and the switching valves are provided; a first synthesis device that is one of the plurality of synthesis devices synthesizes the hydrocarbon gas using a catalyst from the carbon monoxide gas and the hydrogen gas discharged from a first electrolysis device that is one of the plurality of electrolysis devices; a second synthesis device which is another one of the plurality of synthesis devices synthesizes the hydrocarbon gas using a catalyst from the carbon monoxide gas and the hydrogen gas discharged from a second electrolysis device which is another one of the plurality of electrolysis devices; the control device controls a first oxygen path switching valve to switch between discharging the oxygen gas from the first electrolysis device to an oxygen discharge unit and supplying the oxygen gas from the first electrolysis device to the second electrolysis device; the control device controls a second oxygen path switching valve to switch between discharging the oxygen gas from the second electrolysis device to the oxygen discharge unit and supplying the oxygen gas from the second electrolysis device to the first electrolysis device; a first switching valve, which is one of the plurality of switching valves, selectively switches whether or not the oxygen gas, which is secondarily generated by the electrolysis in the second electrolysis device and is supplied to the first electrolysis device by the control device controlling the second oxygen path switching valve, is supplied from the first electrolysis device to the first synthesis device; a second switching valve, which is another one of the plurality of switching valves, selectively switches whether or not the oxygen gas, which is secondarily generated by the electrolysis in the first electrolysis device and is supplied to the second electrolysis device by the control device controlling the first oxygen path switching valve, is supplied to the second synthesis device; when the concentration of the hydrocarbon gas in the exhaust gas discharged from the first synthesis device falls below a predetermined hydrocarbon concentration threshold while the carbon monoxide gas and the hydrogen gas are supplied to the first synthesis device, the control device controls the first switching valve to supply the oxygen gas to the first synthesis device; an electrolytic synthesis system in which, when the concentration of the hydrocarbon gas in the exhaust gas discharged from the second synthesis device is below a predetermined hydrocarbon concentration threshold while the carbon monoxide gas and the hydrogen gas are supplied to the second synthesis device, the control device controls the second switching valve to supply the oxygen gas to the second synthesis device.

Images